There was a run of shows at the Winterland in October (?) of '78 immediately following the Egypt shows. Maybe the sitarist was someone they brought back home with them. More information could be available by using that as a starting point for research.
late hamza el din opened for dead on 78-10-21&22, winterland. he used to play tar (traditional sudanese hand drum) and oud - traditional sudanese string instrument, which does sound like sitar occasionally. in the middle of ollin arageed jerry and dead moved in on both nights. awesome jamming